Electronic thermometer systems are initially relatively expensive compared to mercury thermometers but over their useful life they cost considerably less to use and are less consuming of the time of scarce and expensive medical personnel. Since these thermometers are electronic they require electrical power for their operaton which is supplied in the form of batteries to promote the portability of the electronic thermometer systems. The system requires substantial electrical power to operate the sensing and measuring circuits and to operate the display. Periodically the batteries are removed and replaced with new ones at additional cost or the system is removed from service while the batteries are recharged. Poorer battery duty cycles result if the user habitually unnecessarily extends the measuring and display period or inadvertently fails to switch off the system at the end of its use.
Recently an automatic on/off electronic switch was developed, U.S. Pat. No. 3,965,743, which upon momentary operation of an actuator locked on and turned off automatically after a predetermined interval of time, and it has performed adequately to conserve battery power. However, this prior automatic on/off electronic switch had some shortcomings. There was no way to extend the temperature display period: subsequent operation of the actuator either during the display or after it ended simply restarted the entire thermometer cycle with a re-measurement and display of temperature. In addition the time interval for the temperature display was controlled by an RC network. Since the time interval was nominally 10 seconds the capacitor used was a large, usually tantalum capacitor whose value was less than precise and often resulted in the interval reaching 15 or even 20 seconds. This caused serious difficulty in estimating battery life and maintaining all thermometers operative by means of timely battery recharging or replacement.